In some games of strategy, you need to make your characters evolve to send them to fight or to do different actions.
When you make them evolve, you have choices to make. These choices will determine what the sequel to your game is and if you are gonna loose or win.
If you make wrong choices, characters or creatures you'll make evolve could not be powerful enough. Similarly, if you increase only the attack and not the defence, this could cost you your victory.